The present invention relates to a catalytic method for concentrating isotopes. A more particular application of the method relates to concentrating deuterium using catalysts capable of selectively catalyzing a reaction with a deuterium-containing compound. The present invention finds particular utility in the production of heavy water.
Certain desired isotopes occur naturally but are found only in very low concentrations. There has been a long-felt need to find an efficient and economical process whereby a desired isotope can be concentrated in a substance which contains or is capable of containing the same.
For example, hydrogen-containing substances contain at least two isotopes of hydrogen, namely protium, having an approximate atomic weight of one, and deuterium, having an approximate atomic weight of two. The natural abundance of deuterium in hydrogen gas is given as 0.0150 percent in the "Handbook of Chemistry and Physics," 49th edition (1968-69), published by the Chemical Rubber Company, Cleveland, Ohio. The deuterium present in hydrogen gas is largely in the form of hydrogen deutride (HD) with a much smaller percentage occurring in the form of molecular deuterium (D.sub.2). The deuterium content present in natural, untreated water is usually within the range of 0.012 to 0.016 percent depending on the source of the untreated water. The deuterium present in water is largely in the form of hydrogen deuterium oxide (HDO) with a much smaller percentage occurring in the form of deuterium oxide (D.sub.2 O).
Electrolysis was the first method used commercially to concentrate deuterium. When water is decomposed electrolytically into hydrogen and oxygen, the deuterium content at the cathode is substantially lower than that of the water remaining in the cell. As electrolysis continues, the remaining water becomes progressively enriched in deuterium.
Fractional distillation was another of the early processes used to concentrate deuterium. This process uses differences in vapor pressures to separate deuterium oxide from water.
Several processes have also been described for exchanging isotopes between a fluid and an isotope-containing gas. In U.S. Pat. No. 2,690,379 to Urey et al., processes for accelerating deuterium exchange reactions between liquid water or water vapor and hydrogen gas are described using certain supported metal catalysts. The Urey et al. patent describes several countercurrent and co-current hydrogen exchange systems which are promoted by those catalysts.
In U.S. Pat. No. 2,787,526 to Spevack, a process for concentrating isotopes in water using liquid water and an isotope-containing gas in counter-current flow is described employing reactors which operate at different temperatures. The Spevack patent also describes the use of catalysts to accelerate the exchange reaction.
Neither Urey et al. nor Spevack, however, uses catalysts to selectively catalyze a reaction with an isotope or a isotope-containing compound. Instead, these processes simply use catalysts to accelerate equilibration.
Each of these prior art processes for the concentration of isotopes is extremely expensive. They each require massive quantities of energy or huge processing facilities or both. To date, a process for the concentration of isotopes, such as deuterium, using only moderate quantities of energy and requiring only limited processing equipment has not been developed.